docs: def redshift(self, z):
          """Apply redshift to the flat spectrum.
  
          Unlike :meth:`SourceSpectrum.redshift`, the redshifted spectrum
          remains an analytic flat source.
  
          Parameters
          ----------
          z : number
              Redshift value.
  
          Returns
          -------
          ans : `FlatSpectrum`
  
          """
          tmp = SourceSpectrum.redshift(self, z)
          ans = FlatSpectrum(tmp.flux.max(), fluxunits=tmp.fluxunits)
          return ans